1. Field of the Invention
The present invention relates to air intake ducts. More particularly, the present invention relates to intake ducts for the combustion air of an internal combustion engine in an automobile.
2. Description of the Related Art
Air intake ducts configured with a porous wall are known according to the known prior art. The porous walls provide for better acoustic characteristics because the acoustical resonance of the air column delimited by the porous wall are largely dampened, unlike known plastic ducts with rigid and impervious walls. Indeed, pulses corresponding to the resonance frequencies within the air column may propagate to the outside by traversing the porous wall, which diminishes the intensity of the respective pressure and speed antinodes.
However, air intake ducts configured with porous walls according to the known prior art feature many disadvantages. Firstly, the porous wall is permeable to the warm air located for instance under the engine hood. The warm air arriving within the cylinders after permeating the porous wall is detrimental to the power and/or torque performance of the engine. Secondly, ducts with porous walls of the known art feature some coarseness, from which a loss of load arises by means of the ducted air rubbing against the coarse wall thereof. Finally, it is necessary to include a very wide plastic oversleeve in such air intake ducting systems in order to obtain a sufficient imperviousness when immersed in water, which is very detrimental from an acoustical and style point of view, as well as with regard to the thermal ageing of the plastic material. Alternatively, it is imperative to soak the fibrous material forming the porous wall with a fluoride-based resin, which is an expensive and complicated solution from an industrial point of view and does not provide a uniform imperviousness over all the areas of the duct wall.
The present invention overcomes the disadvantages of ducts configured with a porous wall according to the known prior art by providing an air intake duct configured with acoustical characteristics as good as those of the ducts of the known prior art, but which is impervious to any external fluid (warm air or water), and features a minimal loss of load along the duct and is less expensive than the impervious acoustical ducts of the known prior art.